Electrical resistor and method of making same



Dec. 31, 195T N. PRlTlKlN ETAL 2,818,354

ELECTRICAL RESISTOR AND METHOD OF MAKING SAME Filed Dec. 17, 1954 UnitedNathan Pritikin, Chicago, and Robert Camp, Beerfieid, 111.; said Campassignor to said Prltikm Application December 17, 1954, Serial No.475,938

22 Claims. (Cl. 117-211) This invention relates to an electric resistorand to a method of making such a resistor. It is an object of thisinvention to provide an improved resistor and an improved method ofmaking the same.

So-called iridized coatings of various metal oxides have been employedin the past for resistors, particularly transparent heating elements.These have been successfully employed in Windshields, the heatobtainable by passing a current through the transparent coating beingemployed to keep the windshield free of ice. They have also beenemployed successfully in space-heating elements, a relatively largesheet of glass having any desired pattern of metal oxide depositedthereon. In applications such as these, slight variations in theresistance of the iridized coatingsis not objectionable since theobjective is a reasonable amount of heat distributed with reasonableuniformity over the surface of the glass, or other base, to which theiridized coating adheres.

The application of iridized coatings to resistors of the type commonlyemployed in electronic apparatus has been limited because of a lack ofsuitable means for protecting the iridized coating from the atmosphere.Because of the fact that iridized coatings have certain veryadvantageous characteristics as applied to resistors of the typecommonly employed in electronic apparatus, namely, small temperaturecoefficient of resistance, and stability (when not subjected to theatmosphere), various attempts have been made to find a suitableprotective coating for iridized coatings. All of these attempts havebeen unsuccessful because the protective coatings applied to theiridized coating either were subject to rapid decomposition (especiallyunder severe conditions of temperature and humidity) or permitted thepassage therethrough of small amounts of moisture and oxygen.

The present invention contemplates the application of a protectiveinorganic film fused to the iridized coating. While the invention isparticularly applicable to resistors of the type commonly employed inelectronic apparatus it has application to other uses of iridized filmsand is to be given this broader interpretation except where it isotherwise specified.

It is another object of the present invention to provide an improvediridized coating resistor in which the iridized coating is effectivelysealed against the atmosphere. It is another object of the invention toprovide an improved method for making such a resistor.

It is another object of the invention to provide an improved iridizedcoating resistor which is substantially hermetically sealed. It isanother object of this invention to provide an improved method of makingsuch a resistor.

It is another object of the invention to provide an improved electricalresistor in which an iridized coating resistance film is effectivelyprotected from the atmosphere by an inorganic film fused thereto. It isanother object to provide an improved method for making such aresistor.-

' tates Ptent This invention, together with further objects andadvantages thereof, will be best understood by reference to thefollowing description taken in connection with the accompanying drawingand its scope will be pointed out in the appended claims.

In the drawing, in which like parts are designated by like referencenumerals Figure 1 is a plan view of a resistor of the type commonlyemployed in electronic apparatus, in one stage of production;

Fig. 2 is an enlarged elevational view of one portion of the partiallycompleted resistor of Fig. 1;

Figs. 3 and 4 are views similar to Fig. 2, but showing the resistor insuccessively more complete stages of production;

Fig. 5 is an elevational view of the resistor element of Pig. 4 in acomplete resistor construction; and

Fig. 6 is a view similar to Fig. 3, but showing an alternateconstruction.

In the drawing the invention is shown applied to an electrical resistorof the type commonly employed in electronic apparatus. The invention isparticularly applicable to this type of resistor since this type isfrequently required to have certain operating characteristics which canbe obtained only if the resistance film is well protected from theatmosphere. However, as indicated above, the invention has applicationto other types of resistors (including heating resistors of varioustypes) since in most cases it is desirable that the resistance film beprotected from outside influences, both atmospheric and mechanical.

The resistance element shown in Figs. 1 and 2 includes a glass sheet 10having spaced apart terminals 11 secured to one face thereof. Alsoadhering to the same surface of the glass sheet 10 is an iridizedcoating 12. In Fig. 3 a thin layer of glass frit 13 is shown applied tothe exposed surface of the iridized coating 12, and in Fig. 4 the layerof glass frit is shown fused to form a continuous film 13a over theiridized coating.

In Fig. 5 the glass sheet 10 with its adhering films and terminals isshown assembled with a second glass sheet 20, having terminals 21adhering thereto opposite the terminals 11. Arranged between theterminals at one end of the two glass sheets is a lead 22. This lead ispreferably soldered to the two terminals 21 in order to provide a strongover-all assembly. Preferably, the space between the two glass sheets 10and 20, which is not occupied by the leads 22 and the adjacent solder,is filled by a third glass sheet 23. It will be understood that a lead22 is arranged at each end of the assembly.

The general assembly of Fig. 5 is disclosed in detail and is claimed inapplication Serial No. 463,303 entitled, Electrical Component and Methodof Making Same, filed October 19, 1954, by the same inventor. Since theparticular assembly in which a resistor constructed in accordance withthe present invention may be incorporated does not in itself constitutea part of the present invention, the assembly is not described infurther detail herein.

The iridized coating 12 shown in Figs. 1 and 2 may be of tin oxide or ofany of the various other metal oxides which form a suitable resistancefilm of high or low resistance per square. Such metal oxide films aregenerally produced by mixing a salt of the desired metal in a liquidcarrier and by spraying this on a heated glass sheet. The resultingiridized coatings are generally accepted as being formed primarily ofthe metal oxide, although there is some difference of opinion as to theexact composition. For the purposes of this application, films of thistype are referred to herein as iridized coatings of metal oxides.

This expression is intended merely to indicate this gen eraltype ofcoating and is not to be considered as being limited to any particularmolecular arrangement or configuration.

It is believed, for example, that some authorities contendithat theseso-called iridized coatings of metallic oxides contain the, metal andoxygen elements in an arrangement which. does not constitute a trueoxide of metal. Other authorities contend; that these coatings arepartially metal oxides and partially metal in a pure state or incombination with-other elements. Accordingly, the expression iridizedcoating of metal oxides is intended to include thisgeneraltype.ofxcoating regardless of whether the coatingis actuallyapropenmetal oxide, speaking in strict chemical terms.

.Various metals are frequentlycmployed in the production of suchiridized coatings. These include,=but are not limited to, tin, indium,-cadmium,.andvarious combinations of these three, with or witlioutsmalladditional quantities of zinc, copper, iron, magnesium, cobalt, andvanadium. Metals are selectedfor .usein iridized coatings according tothe desiredicharacteristics of coatings. Some of. the mostpopular metalsare tin, tin and antimony, and indium.

Since the presentinvention isnotconcernedprimarily with theselection ofaparticular metal'for forming-an iridized coating, the choice of metalsis1not considered furtherherein.

The base 10, as shown .in the drawing, .is indicated above as .being ofI glass. Itlmay be ,of ordinary window glass, theat-resistantglass suchas Pyrex, ceramics, or-any other inorganic insulating material. .Thebase should have a smooth, nonporous surface and should meet thephysical requirements called for .by the application .of the ultimateresistor. For the purpose of this application, the base is, of course,the material actually contacting the iridized coating and might be, forexample a glass film or other glaze on an underlying metallicfoundation.

The glass frit 13, shown in Fig. 3, may be a conventional fritobtainable on the market. Where the resistor is to be subjected tosubstantial changes in temperature-it is recommended that the frit havea temperature coefficient of expansion nearly equal to or slightly lessthan that of the base 10. In general the frit must be fusible underapplied heat which will not be detrimental to the iridized coating 12,the terminals 11 or the base 10. By employing rapid heating of the frit,it is possible to fuse the frit without damage to the other components,and particularly the base 10, even though the material of the base mayhave substantially the same melting temperature as the frit. The fritmust melt to such an extent that the particles n the frit fuse togetherto form a continuous film. Heat maybe applied rapidly and for only ashort time, whereby only some portion of the frit melts or softens.Particularly the outer surfaces of the individual particles soften,whereas the inner core of each particle might remain substantiallysolid. The only essential for complete protection of the iridizedcoating is that the frit be fused to form a continuous film, fused tothe iridized coating. In view of this, differing materials may beincorporated in the frit, and all of the materials in the frit need notmelt or fuse at the same temperature. Again, all that is essential forcomplete protection of the iridized coating is that a sufficient portionof the frit be melted or softened that a continuous film be formed andfused to the iridized coating. Accordingly, the frit may have thecharacteristics of what is commonly termed a ceramic. When the termglass frit is employed herein, it is intended to encompass any inorganicnonconducting frit of which a sufficient proportion will melt or softenat a reasonable temperature to cause the formation of a continuous film,fused to the iridized coating.

Several references are made above to a continuous film. Obviously, theword continuous is meant to aply to the fine structure of the filmrather than to its overall arrangement. More specifically, a continuousfilm refers to one in which adjacent particles of frit are melted orfused to a sufficient extent that the melted material bridgessubstantially continuously between adjacent particles wherever the fritis applied. The over-all pattern of the frit as applied may becontinuous or discontinuous in different applications.

The frit may be deposited on the iridized coating in any desired manner,but it has been found to bepractical to use a screening process. In thiscase the frit is mixed with a carrier such as 5% ethyl cellulose andpine oil. The overall mixture may be 25 %'carrier and 75 frit or to thedesired consistency. For convenience in handling, the pine oil may beallowed'toevaporate or may be baked out. All elements-of thesuggestedcarrier are either evaporated or burned up when subsequently subjectedto temperatures which fuse the frit.

The frit should be applied heavily enough to provide a fused film of thedesired th1ckness,'itbeing understood that the fused film will-beconsiderably thinner than the applied frit. A film of four milsthickness is recommended for applications where normal voltages areencountered. The film can, however, be made much thinner or thicker'where desired. I

.In the embodiment of the invention'disclosed in Figs. l-5,theterminals11 are shown applied'to the base 10 before the application'ofthe'iridized coating 12, since the terminals are'shown'to underlie theextremities of the iridized coatings. Alternatively, however, and asshown in Fig. 6, the iridized coating 13 may be appliedfirst, followedby application of the terminals 11'. In this case, parts of theterminals 11' overlie the extremities of the iridized coating 13. Thereis believed to be little, if any, difference between these alternativesin so far as performance and ease of production are concerned. In eithercase, the terminals and theiridized coating must be either applied in.thedesired'patterns or must be reduced to the desired patterns afterapplication to the entire surface. Attention is directed to the factthat :some difficulty has been encountered informing the iridizedcoating on a silver terminal. Accordingly, if the terminals are to beapplied first, as in Figs. 1-5, a metal more noble than silver isrecommended. On the other hand, if the iridized film is applied first,as in Fig. 6, silver terminals have been found to make good contacttherewith.

Referring to one specific embodiment of the invention known to .besatisfactory, the baselt) is composed of ordinary window .glass, and theiridized coating 12 is primarily tin oxide. The iridized coating isetched away to provide areas for application of the terminals. Thelatter comprise glass .frit and metallic silver and are fused to theglass base 10 and overlie the ends of the iridized coating. It has beenfound that satisfactory electrical connection is thereby made betweenthe terminals and the iridized coating, and that leads 22 may besoldered to the terminals to provide a mechanically strong construction.The glass frit for covering the iridized coating is a lead boro silicateglass containing 69% lead oxide, 9% boron oxide, and 22% silica.

In accordance with another embodiment of the invention, the glass film13a is produced by spraying. In this case the resistor element of Fig. 2is subjected to a spray of molten glass, producing the resistor elementof Fig. 4 directly.

Apparatus for spraying molten glass onto the resistor element of Fig. 2may be substantially identical to that commonly employed for sprayingmolten metals. Attention is directed, however, to the fact that moltenglass has a very corrosive reaction on any metal which is susceptible tothe formation of oxides. More specifically, if the metal employed in theconstruction of the spraying apparatus is susceptible to the formationof oxide at the temperature of the molten glass, the molten glasseffectively removes any such oxides whereupon the metal again is exposedto oxidation and subsequent removal of the oxide film. Constantsubjections of such metals to molten glass quickly destroy the metal.Accordingly, any portion of the spraying apparatus which is subjected tothe molten glass should be plated with platinum. A very thin film ofplatinum is generally recognized as being strongly resistant tocorrosion by molten glass.

Preferably, the resistor element of Fig. 2 is heated be-- fore beingsubjected to the spray of molten glass, and more particularly, is heatedbeyond the strain point of the base 10. However, some experimentssuggest that if the spray of molten glass is sufficiently hot, the basemay be unheated.

Where it is desired that certain areas, such as portions of theterminals 11, not be covered by the glass film, these may be shieldedfrom the spray of molten glass by various obvious means including, forexample, an independent mask arranged closely adjacent the resistorelement, or a removable mask such as tape or an emulsion applieddirectly to the portions of the terminals 11 which are not to be coatedwith the glass film.

Attention is directed to the fact that while molten glass has a verycorrosive reaction on most metals because of the fact that it removesand apparently dissolves any oxide formed on the surface of such metals,the molten glass applied to the iridized metal oxide coating 12 has beenfound to have no substantial efiect thereon. This is in spite of thefact that the iridized metal oxide coating may be on the order ofone-millionth of an inch thick. This would appear to substantiate thecontentions of some authorities that the iridized metal oxide coating isnot a true metal oxide in strict chemical terms. In any event, it hasbeen found, contrary to reasonable assumption, that molten glass,whether sprayed onto an iridized metal oxide film or deposited in theform of frit and subsequently fused, has no deleterious effects on theiridized metal oxide coating.

In accordance with still another embodiment of the invention, a glasssheet may be substituted for the glass frit or the sprayed glass to sealthe exposed surface of the iridized metal oxide coating. In this case aglass sheet is laid over the resistor element of Fig. 2 and is heateduntil it is quite soft. Pressure is preferably applied to bring thesoftened glass sheet into intimate contact with the iridized metal oxidecoating at all points.

Some difiiculty may be encountered in the practice of this embodiment ofthe invention in obtaining intimate contact at all points because of thepresence of air trapped between the glass sheet and the iridized metaloxide coating. However, if any air pocket is entirely isolated, that is,if the edges of the iridized metal oxide coating and the glass sheet arefused together, no substantial harm results from the entrapped air, atleast from the viewpoint of deterioration of the iridized oxide coating.

Preferably the glass sheet employed to seal the iridized metal oxidecoating has a temperature coefficient expansion nearly equal to that ofthe base 10. The glass sheet need not be clear glass but may incorporatematerials which do not soften during its application to the iridizedmetal oxide coating, all as explained above in connection with use ofglass frit.

While particular embodiments of the invention have been shown, it willbe understood, of course, that the invention is not limited theretosince many modifications may be made, and it is, therefore, contemplatedto cover by the appended claims any such modifications as fall withinthe true spirit and scope of the invention.

The invention having thus been described, what is claimed and desired tobe secured by Letters Patent is:

l. The method of making an electrical resistor which comprisesdepositing an iridized coating of metal oxide on a preformed inorganicinsulating base, and fusing a film of glass on the exposed surface ofsaid iridized coating.

2. The method of making an electrical resistor which comprisesdepositing an iridized coating of metal oxide 6 on a preformed inorganicinsulating base, applying glass frit to the surface of said iridizedcoating, and fusing said frit to form a continuous film over saidiridized coating.

3. The method of making an electrical resistor which comprisesdepositing an iridized coating of tin oxide on a preformed inorganicinsulating base, applying glass frit to the surface of said iridizedcoating, and fusing said frit to form a continuous film over saidiridized coating.

4. The method of making an electrical resistor which comprisesdepositing an iridized coating of tin and antimony oxide on a preformedinorganic insulating base, applying glass frit to the surface of saidiridized coating, and fusing said frit to form a continuous film oversaid iridized coating.

5. The method of making an electrical resistor which comprisesdepositing an iridized coating of metal oxide on a heated glass base,applying glass frit to the surface of said iridized coating, and fusingsaid frit to form a continuous film over said iridized coating.

6. The method of making an electrical resistor which comprisesdepositing an iridized coating of tin oxide on a heated glass base,applying glass frit to the surface of said iridized coating, and fusingsaid frit to form a continuous film over said iridized coating.

7. The method of making an electrical resistor which comprisesdepositing an iridized coating of tin and antimony oxide on a heatedglass base, applying glass frit to the surface of said iridized coating,and fusing said frit to form a continuous film over said iridizedcoating.

8. The method of making an electrical resistor which comprisesdepositing a pair of spaced apart terminals and an iridized coating ofmetal oxide on a preformed inorganic insulating base with said iridizedcoating electrically contacting said terminals, applying glass frit tothe surface of said iridized coating, and fusing said frit to form acontinuous film over said iridized coating.

9. The method of making an electrical resistor which comprisesdepositing a pair of spaced apart terminals and an iridized coating ofmetal oxide on a heated glass base with said iridized coatingelectrically contacting said terminals, applying glass frit to thesurface of said iridized coating, and fusing said frit to form acontinuous film over said iridized coating.

10. The method of making an electrical resistor which comprisesdepositing a pair of spaced apart terminals and an iridized coating oftin oxide on a heated glass base with said iridized coating electricallycontacting said terminals, applying glass frit to the surface of saidiridized coating, and fusing said frit to form a continuous him oversaid iridized coating.

11. The method of making an electrical resistor which comprisesdepositing a pair of spaced apart terminals and an iridized coating oftin and antimony oxide on a heated glass base with said iridized coatingelectrically contacting said terminals, applying glass frit to thesurface of said iridized coating, and fusing said frit to form acontinuous film over said iridized coating.

12. The method of making an electrical resistor which comprises sprayinga metal salt in a liquid carrier on a heated glass base, applying glassfrit to the surface of the resulting iridized coating, and heating saidfrit to fusing temperature to form a continuous film over said iridizedcoating.

13. The method of making an electrical resistor which comprisesdepositing an iridized coating of metal oxide on a glass base, applyinga glass frit having substantially the same temperature coefficient ofexpansion as said glass base to said iridized coating, and fusing saidfrit to form a continuous film over said iridized coating.

14. The method of making an electrical resistor which comprisesdepositing an iridized coating of metal oxide on a preformed inorganicinsulating base, and spraying molten glass on the surface of saidiridized coating.

15. The method of making an electrical resistor which comprisesdepositing an iridized coating of tin oxide 7 on a preformed inorganicinsulating base, and spraying molten glass on the surface of saidiridized coating.

16. The method of making an electrical resistor which comprisesdepositing. an iridized coating of tin and antimony oxide on a preformedinorganic insulating base, and spraying molten glass on the surface ofsaid iridized coating.

17; The method of making an electrical resistor which comprises sprayinga metal 'salt in a liquid carrier on a heated glass base, and sprayingmolten glass on the surface of the resulting iridized coating.

18. The method of making an electrical resistor which comprisesdepositing an iridized coating of metal oxide on a'gla'ss base, laying asheet of glass over said coating, and heat softening said sheet to fuseit to said coating.

19. An electrical resistorcom prising a preformed base of inorganicinsulating material, an'iridize'd metal oxide resistance film" on saidbase, and a continuous, unitary gl ass'film secured in intimatemolecularcontact to the surface of said resistance film:

20'. An electrical resistor comprising a preformed base of inorganicinsulating material, an iridized tin oxide resistance film on saidbase,and a continuous, unitary glass film secured in'intimate molecularcontact to the surface of said resistance film.

21. An electrical" resistor comprising a preformed base of inorganicinsulating material, an iridized tin and antimony oxide resistance filmon said base, and a continuous, unitary glass film secured in intimatemolecular contact to the surface of said resistancefilm.

22. An electrical resistor comprising a preformed base' References Citedin the file of this patent UNITED STATES PATENTS Re. 23,556 Mochel Sept.30, 1952 2,154,387 Sleeman Apr. 11, 1939 2,238,031 Brennan Apr. 15, 19412,289,921 Massa July 14, 1942 2,489,127 Forgue Nov. 22, 1949 2,564,707Mochel Aug. 21, 1951 2,614,944 Lytle Oct. 21, 1952 2,648,752: SaundersAug. 11 1953 2,648,753 Lytle- Aug. 1.1, 1953 2,717,946 I Peck Sept. 13,1955 a U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OFCORRECTION Patent No 2,818,354 December 31, 1957 Nathan Pritikin et all&

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 5, line 54, before "oxide" insert --metal--; column 8, line 9,after "continuous" inser unitary--.,

Signed and sealed this 4th day of March 1958.

(SEAL) Atfiest:

KARL H, AXLINE ROBERT C. WATSON Attesting Officer Conmissioner ofPatents Disclaimer 2,818,354.Nathcm Pm'zfz'lcin, Chicago, Ill.ELECTRICAL RESISTOR AND METHOD OF MAKING SAME. Patent dated Dec. 31,1957. Disclaimer filed June 30, 1961, by the assignee, lntellum, Inc.

Hereby enters this disclaimer to claims 14,15, 16, and 17 of saidpatent.

[Ofiaz'al Gazette August 8, 1961.]

UNITED STATES PATENT OFFICE Certificate Patent No. 2,818,354; PatentedDecember 31, 1957 Nathan Pritikin and Robert C. Camp Application havingbeen made jointly by Nathan Pritikin and Robert C. Camp, the inventorsnamed in the patent above identified, for the issuance of a certificateunder the provisions of Title 35, Section 256 of the United States Code,deleting the name of the said Robert C. Camp from the patent as a jointinventor, and a showing and proof of facts satisfying the requirementsof the said section having been submitted, it is this 25th day of July1961, certified that the name of the said Robert C. Camp is herebydeleted from the said patent as a joint inventor With the said NathanPritikin.

[SEAL] EDWIN L. REYNOLDS, First Assistant Commissioner of Patents.

1. THE METHOD OF MAKING AN ELECTRICAL RESISTOR WHICH COMPRISESDEPOSITING AN IRIDIZED COATING OF METAL OXIDE ON A PREFORMED INORGANICINSULATING BASE, AND FUSING A FILM OF GLASS ON THE EXPOSED SURFACE OFSAID IRIDIZED COATING.
 15. THE METHOD OF MAKING AN ELECTRICAL RESISTORWHICH COMPRISES DEPOSITING AN IRIDIZED COATING OF TIN OXIDE ON APREFORMED INORGANIC INSULATING BASE, AND SPRAYING MOLTEN GLASS ON THESURFACE OF SAID IRIDIZED COATING. 18 THE METHOD OF MAKING AN ELECTRICALRESISTOR WHICH COMPRISES DEPOSITING AN IRIDIZED COATED OF METAL OXIDE ONA GLASS BASE, LAYING A SHEET OF GLASS OVER SAID COATING, AND HEATSOFTENINGN SAID SHEET TO FUSE IT TO SAID COATING.